1. Field of the Invention
This invention relates to a clean air supply means in a clean tunnel.
2. Description of the Prior Art
To convey semiconductor wafers or the like by a self-running truck in a clean tunnel, the clean tunnel must be constantly filled with a clean air. In FIG. 5, there is shown a conventional clean air supply means for supplying a clean air into a clean tunnel 1 of a rectangular section.
The clean tunnel 1 is provided with a frame body 2 having an air flow passage 2k at its upper end and an air filter 3 thereunder. Any type of air filter having high filtering efficiency may be employed. A plurality of air inlets 4 spaced with each other are disposed along a side wall 2s of the air flow passage 2k. The air is supplied into the air flow passage 2k through the plurality of air inlets 5 by means of an outside air blower (not illustrated). Subsequently, a clean air filtered by the air filter 3 is blown as a laminar layer in a tunnel zone where a travelling rail 5 is laid on a bottom plate 2b of the frame body 2. Then, the clean air is discharged from a plurality of air outlets 6, each of which is bored at a center of the bottom plate 2b as well as the travelling rail 5. The clean air is discharged by an air discharge blower (not illustrated).
An air supply system of this conventional clean tunnel will be described with reference to FIG. 6.
An air supply blower 7 is provided with a main duct 8 disposed in parallel with the clean tunnel. The main duct 8 has a plurality of subducts 9 communicated with respective air inlets 4. Likewise, an air discharge blower 13 is also provided with a main duct 12 disposed in parallel with the clean tunnel. The main duct 12 has a plurality of subducts 11 communicated with the air outlets 6. Thus, any dust that may occur in connection with driving of a self-running truck 15 can be discharged, together with the clean air, from the plurality of air outlets 6.
The disadvantage of this prior art is that the piping system is of a complicated construction and the clean tunnel itself becomes large-size. In addition, the air flow speed within the tunnel is irregular and the clean air is susceptible to be mixed with dust. Thus, a large quantity of clean air are discharged outside wastefully.